System for heat treatment of a feed material

ABSTRACT

A method for heat treatment of a grain-shaped feed material using a calcination device to remove carbonate or water of crystallization from the feed material are provided. To continuously check the quality of the heat treatment process, the bulk density of the heat-treated material is measured continuously, wherein upon detection of a deviation of the determined bulk density from the at least one desired bulk density at least one heat treatment parameter of the heat treatment is adapted automatically or manually.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of and claims priority to andthe benefit of co-pending U.S. application Ser. No. 16/276,410, filedFeb. 14, 2019, which is a division of U.S. application Ser. No.15/315,378, filed Nov. 30, 2016, now U.S. Pat. No. 10,233,118, which wasa national stage of PCT/AT2015/050142 filed Jun. 5, 2015, which claimspriority to Austrian Application No. GM 50088/2014, filed Jun. 5, 2014,all of which are incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to a method for the expansion of sand grain-shapedraw material in which the raw material drops downwards through asubstantially vertical heated shaft provided with means for forming atemperature profile, in which a shaft flow prevails wherein as a resultof heat transfer in the shaft, the raw material expands to form expandedgranulate and the granulate formed is passed into a pneumatic conveyingline with a conveying flow for further transport, as well as to anapparatus which comprises a separating device, preferably a gas cyclonewhich can be connected to a pneumatic conveying line.

The invention also relates to a method for heat treatment of agrain-shaped feed material wherein a first material flow containing thegrain-shaped feed material is fed into one end of a calcination devicewherein the grain-shaped feed material undergoes a heat treatment withinthe calcination device in order to produce grain-shaped heat-treatedmaterial by removing water of crystallization or carbon dioxide from thegrain-shaped feed material; wherein a second material flow containingthe grain-shaped heat-treated material is released from a second end ofthe calcination device.

BACKGROUND OF THE INVENTION

A method for producing an expanded granulate from sand grain-shaped rawmaterial is disclosed in WO 2013/053635 A1, where the object consists inadjusting a closed surface of the expanded granulate in a controllablemanner so that the expanded granulate exhibits no hygroscopicity orhardly any hygroscopicity. In addition, the possibility of specificallyinfluencing the surface structure of the expanded granulate andtherefore the roughness is to be provided. To this end, this documentproposes providing a plurality of independently controllable heatingelements arranged along the drop section of the sand grain-shaped rawmaterial and performing a temperature detection along the drop section,wherein the heating elements are controlled depending on the detectedtemperature below the region in which the expansion process takes place.Removal of the expanded granulate from the lower end of the drop sectionis ensured by means of a pneumatic conveying line into which the dropsection opens.

As a result of the vertical alignment of the shaft and as a result ofthe additional introduction or extraction of process gases accompanyingthe expansion process, flows occur inside the shaft which act on thesand grain-shaped raw material. In particular, the formation of anear-wall upwardly directed boundary layer flow has a positive effect onthe quality of the expansion process since this boundary layer flowprevents any baking of the sand grain-shaped raw material on the wall ofthe shaft. If the expansion shaft is closed towards the top, in additionto the upwardly directed boundary layer flow, a central downwardlydirected core flow is established. This core flow prevents some of theabove-described boundary layer flow and therefore results in baked-ondeposits. The influence of the core flow can be reduced by thehitherto-known extraction/in-blowing of process gas from/into the headregion of the shaft.

Such above-described baked-on deposits on the shaft walls has the resultthat the heat transfer from the shaft walls to the raw materialdeteriorates. In addition, this results is a detachment of the boundarylayer flow which leads to additional baked-on deposits in other regionsof the shaft. As a result, the quality of the expansion processdeteriorates appreciably and the fraction of undesired, unexpandedgranulate leaving the shaft is increased.

Since the sand grain-shaped raw material is a naturally occurring rawmaterial, this has fluctuations in its composition, for example, in thefraction of propellants. This has the result that at constant processparameters, possibly during the formation of a specific temperatureprofile in the shaft by the variously controllable heating elements, thequality of the expansion process depending on the condition of the rawmaterial is not constant.

In known processes the quality of the expansion process is only measuredon a random sample basis and the process is then re-adjusted or stopped.

It can thus be seen to be a disadvantage of the prior art that neitherthe fluctuating composition of the sand grain-shaped raw material northe formation of baked-on deposits can be detected promptly, which ineach case results in a deterioration of the quality of the end productsince the fraction of the unexpanded granulate increases or the desiredproperties of the expanded granulate are not achieved.

DE 6608156 U relates to a device for determining the litre weight ofcombustion material, wherein a container connected to a weighing deviceis filled continuously via a double vibrating sieve and combustionmaterial can be discharged continuously from the container by means of adischarge device.

Calcination devices are known to be used for thermal decomposition ofvarious materials such as carbonate ores, e.g. limestone, or hydratedminerals, e.g. gypsum. In the calcination device the feed materialundergoes a heat treatment by which carbon dioxide or water ofcrystallization is removed from the feed material either in gaseous formor as steam.

SUMMARY OF THE INVENTION

One object of the invention is to provide a method for producing anexpanded granulate from sand grain-shaped raw material and a device formeasuring the bulk density, which does not have the describeddisadvantages and ensures that the quality of the expansion process iscontinuously monitored. The method should ensure trouble-free andlow-maintenance operation. The device should be characterized by asimple and reliable design. Furthermore, it should be possible toretrofit the invention to existing systems without major expenditure.

This object is achieved by the method mentioned initially whereby thebulk density of the expanded granulate is measured continuously, whereinupon detection of a deviation from at least one defined bulk density,the temperature profile in the shaft is automatically or manuallyadjusted and/or the feeding of raw material into the shaft is reducedautomatically or manually.

The invention is based on the fact that as a result of a continuousmeasurement of the bulk density, the quality of the expansion process iscontinuously monitored. If the bulk density changes, the expansionprocess can be adapted accordingly. This can be accomplished on the onehand, whereby a signal, for example, a warning tone, notifies the userthat an adjustment of the process is required or on the other hand, byan automated processes wherein the system automatically adapts theprocess according to predefined parameters.

If a fluctuation condition of the raw material is determined on thebasis of the variation of the bulk density, this can be compensated byadapting the temperature profile in the shaft. If however baked-ondeposits in the shaft are determined as a result of the measurement, thefeeding of raw material can be reduced, preferably stopped in order toprevent further baked-on deposits in the shaft and thus minimize therepair expenditure.

With regard to the sand grain-shaped raw material, not only mineralsands can be used in which water is bound as propellant such as, forexample, pearlite or obsidian sand. This can also comprise mineral dustwhich is mixed with water-containing mineral binder where in this casethe water-containing mineral binder acts as propellant. The expansionprocess can in this case proceed as follows: the mineral dust whichconsists of relatively small sand grains having a diameter of, forexample, 20 μm, forms larger grains of, for example, 500 μm with thebinder. At a critical temperature the surfaces of the sand grains of themineral dust become plastic and form closed surfaces of the largergrains or melt to form such. Since the closed surface of an individuallarger grain is usually overall smaller than the sum of all the surfacesof the individual sand grains of the mineral dust which are involved inthe formation of this larger grain, in this way surface energy is gainedor the ratio of surface to volume decreases. At this moment, largergrains each having a closed surface are present where the grainscomprise a matrix of mineral sand dust as well as water-containingmineral binder. Since the surface of these mineral grains as previouslyare plastic, the forming water vapour can subsequently expand the largergrains. That is, the water-containing mineral binder is used aspropellant. Alternatively mineral dust can also be mixed with apropellant, where the propellant is blended with mineral binder whichpreferably contains water. CaCO₃ for example can be used as propellant.In this case, the expansion process can take place similarly to thatdescribed above: the mineral dust which has a relatively small sandgrain size (for example, 20 μm diameter) forms larger grains (forexample, 500 μm diameter) with the propellant and the mineral binder.Upon reaching a critical temperature, the surfaces of the sand grains ofthe mineral dust become plastic and form a closed surface of the largergrains or fuse to form such. The closed surfaces of the larger grainsare plastic as previously and can now be expanded by the propellant. Ifthe mineral binder is water-containing, this can function as additionalpropellant. Thus, in a preferred embodiment of the method according tothe invention it is provided that the mineral material with propellantcomprises a mineral material in which water is bound and acts aspropellant or mineral dust mixed with water-containing mineral binderwhich acts as propellant or mineral dust mixed with a propellant whichis blended with mineral binder, wherein the mineral binder preferablycontains water and acts as additional propellant. In order to be able tocarry out the method presented as efficiently as possible, in additionto a shaft furnace it is preferable to provide a plurality of heatingzones with (independently of one another) controllable heating elementsas well as an intelligent regulating and control unit. This controls theheating elements preferably as a function of measured temperatures alongthe furnace shaft.

According to a preferred embodiment, the conveying flow is produced byan extraction device. If the extraction device is attached at the end ofthe conveying line facing away from the shaft, a conveying flow isobtained over the entire length of the conveying line, where otherelements such as, for example, filter systems can be attached in theconveying line.

In another embodiment, it is provided that the expanded granulate isseparated from the conveying flow in the conveying line by a separatingdevice, preferably a gas cyclone. By attaching a separating device inthe conveying line, it is possible to separate the expanded granulate.Since the expanded granulate comprises the end product of the method,the concentrated removal from the conveying flow, in particular by a gascyclone, is advantageous since this can be connected to a container suchas, for example, a silo.

In a further preferred embodiment, the bulk density of the granulateseparated by the separating device, in particular the gas cyclone ismeasured. A measurement at this point of the process is particularlyadvantageous since no additional complex units are required in theconveying line such as possibly optical media or a separate measuringline.

According to a particularly preferred embodiment the separated expandedgranulate is concentrated to form a granulate flow and this is guidedinto a measuring container, wherein the measuring container is connectedto a measuring device to determine the bulk density. In this way, ameasurement of the bulk density is achieved over a defined volume of themeasuring container and the mass weighed by means of the measuringdevice is achieved. In this case, the geometry of the measuringcontainer should preferably be configured very simply, possibly as acylinder or rectangular prism. As a result of the concentrating of thegranulate flow, a uniform filling of the measuring container is ensuredso that this is sufficiently filled even with low utilization of theprocess or a change in the quality of the expansion process is detectedsufficiently rapidly.

A further preferred embodiment provides that a dosing element isprovided between shaft and conveying line, in which the quantity ofgranulate which is transferred from the shaft into the conveying line isregulated by means of means for regulation so that a defined materialaccumulation of the granulate is formed in the dosing element as buffer,which decouples the shaft flow from the conveying flow. This arrangementin particular has positive effects on the shaft flow if the shaft flowis thereby decoupled from the conveying flow since pressure fluctuationsfrom the conveying line, possibly due to the cleaning cycle of a filter,no longer affect the shaft flow and the frequency of baked-on depositsin the shaft can also be reduced as a result.

Further particularly preferred embodiments provide that process air isextracted from the head region of the shaft or that process air is blowninto the head region of the shaft in order to stabilize the part of theshaft flow directed to the head region. This variant achieves aparticularly high quality of the expansion process since as a result ofthe extraction or blowing-in of process air, the flow conditions arestabilized in that no secondary flows promoting harmful baked-ondeposits are promoted.

A device according to the invention for measurement of the bulk densityof the expanded granulate comprises a separating device configured as agas cyclone which can be connected to a pneumatic conveying line,wherein at least one measuring container which has a base surface forreceiving at least a part of the granulate flow from the separatingdevice configured as a gas cyclone is arranged underneath the gascyclone in the operating state, wherein the measuring container isconnecting to a measuring device for determining the bulk density. Ithas proved to be very advantageous if the separating device isconfigured as a gas cyclone although other separating devices are alsofeasible.

This device is based on the fact that the granulate separated by theseparating device (by the gas cyclone) is transferred into a measuringcontainer in order to fill this and keep it filled, wherein the entiregranulate flow need not enter into the measuring container, a partthereof is sufficient. Since the measuring container is locatedunderneath the gas cyclone in the operating state, no further conveyingdevice is required, gravity is sufficient. The bulk density can now bemeasured in a simple manner by means of a suitable measuring deviceusing the defined volume of the measuring container.

In a further preferred embodiment of a device according to the inventionfor measuring a bulk density of the expanded granulate, a means forconcentrating the granulate flow, preferably a funnel, is disposedbetween the separating device configured as a gas cyclone and themeasuring container, whereby a particularly simple concentrating isachieved. As a result of the formation of the concentrated granulateflow, filling of the measuring container is ensured even when littlegranulate is located in the conveying flow.

A further particularly preferred embodiment of a device according to theinvention for measuring the bulk density of the expanded granulateprovides that the measuring container is connected to the measuringdevice via a side arm, whereby a particularly simple positioning of themeasuring container in the granulate flow is achieved which can also beretrofitted to already existing systems.

In a further preferred embodiment of a device according to the inventionfor measuring a bulk density of the expanded granulate, the measuringdevice is configured as a weighing device, preferably as scales. Thissimple form of weight determination allows a technically non-complex andcost-effective measurement of the bulk density and can be installedwithout major additional expenditure.

According to a further particularly preferred embodiment of a deviceaccording to the invention for measuring the bulk density of theexpanded granulate, an overflow for at least a part of the granulateflow is provided on the measuring container. This variant makes itpossible to prevent an accumulation of the granulate flow when themeasuring container is completely full whereby the excess part of theflow can escape from the measuring container, preferably over the edgeof the measuring container.

In a further particularly preferred embodiment of a device according tothe invention for measuring the bulk density of the expanded granulate,the measuring container has openings in the base surface to allow atleast a part of the granulate flow to drain continuously. Thisarrangement ensures that a certain part, preferably 60% of the entireproduction quantity of the expanded granulate, can flow continuouslythrough the measuring container in order to enable a prompt measurementof the bulk density and thus the determination of the expansion quality.

A second object of the intervention is to provide a method for heattreatment of a grain-shaped feed material, especially a calcinationprocess, as well as a system comprising a calcination device and ameasuring device, which ensure that the quality of the calcinationprocess is continuously monitored. The method should ensure trouble-freeand low-maintenance operation. The system should be characterized by asimple and reliable design. Furthermore, it should be possible toretrofit existing systems without major expenditure.

Due to inhomogeneity of the feed material, which can be pre-refined oreor pre-refined mineral material, the composition of the feed material,especially the content of carbonate or water of crystallization, mayvary. Because of the fluctuation of the composition of the feed materialalso the quality of the heat-treated material can vary considerably,when the heat treatment parameters are kept stable and are not adaptedto the current feed material.

In order to be able to monitor the quality of the heat treatment withinthe calcination device continuously and to be able to automatically ormanually adapt at least one of the heat treatment parameters so thatfluctuations in the quality of the feed material can be compensated, itis provided that the bulk density of the heat-treated material producedwithin the calcination device is measured continuously and at least oneof the heat treatment parameters is adapted automatically or manuallyupon detection of a deviation of the determined bulk density from the atleast one desired bulk density. This measure ensures that changes of thecomposition of the feed material can be compensated by the heattreatment in order to maintain a consistent high quality of theheat-treated material. Measurement of the bulk density is particularlysuitable for determining the quality of the heat-treated material, asthe bulk density changes due to the thermal decomposition in thecalcination device as carbon dioxide and/or water of crystallization (inform of steam) are removed from the feed material by the heat treatment.

The method of continuously determining the bulk density itself as wellas the device for measuring the bulk density are designed analogous tothe method and the device described in detail with regard to theexpanded granulate, however, as the grain-shaped heat-treated materialis usually not transported via a pneumatic conveying line, no separationdevice is necessary. Thus the second material flow can be directly fedinto the measuring container or can be conveyed via appropriatemechanical conveying means to the measuring container. Furthermore theheat treatment parameters, such as e.g. temperature, conveying speed orretention time, can be adapted as well as a heat profile, in case thecalcination device is equipped with a plurality of individuallycontrolled heating elements. With regard to the system it shall notremain unsaid that the calcination device replaces the expansion devicedescribed before.

In a further embodiment it is provided that the calcination device isconfigured as a rotary kiln and the grain-shaped feed material and thegrain-shaped heat-treated material respectively are conveyed through therotary kiln continuously.

In a further embodiment of the method it is provided that the secondmaterial flow is concentrated before being directed into the measurementcontainer. For the system it is provided that a means for concentratingthe second material flow is disposed between the release opening of thecalcination device and the at least one measuring container.

In a further embodiment of the method it is provided that thecalcination device comprises a rotary kiln, in which the heat treatmenttakes place, and the grain-shaped feed material as well as thegrain-shaped heat-treated material are conveyed through the rotary kilncontinuously.

In a further embodiment of the method it is provided that the heattreatment parameters contain: (pre-set) heat treatment temperature,(measured) average heat treatment temperature, (measured) minimum heattreatment temperature, (measured) maximum heat treatment temperature,heat treatment temperature profile, heat treatment conveying speedand/or heat treatment retention time.

In a further embodiment of the method it is provided that a heattreatment temperature within the calcination device lies between 250° C.and 1000° C.

In a further embodiment of the method it is provided that upon detectionof a deviation of the determined bulk density from the at least onedesired bulk density a heat treatment temperature within the calcinationdevice is increased.

If the method shall account for variable changes of the bulk densitywith regard to the currently produced heat-treated material instead ofhaving set values for the desired bulk density, it is provided that thedesired bulk density is continuously or periodically adjusted dependingon the actually determined bulk densities in order to detectfluctuations in the bulk density of the grain-shaped heat-treatedmaterial.

In a further embodiment of the system it is provided that the device formeasuring the bulk density is positioned adjacent to the release openingof the calcination device, preferably connected via means for gravitytransport such as a chute.

In a further embodiment of the system it is provided that the device formeasuring the bulk density is positioned underneath the release openingof the calcination device, so that the produced heat-treated material isdirectly fed from the release opening into the measurement container,preferably via a concentration means such as a funnel.

In a further embodiment of the system it is provided that the device formeasuring the bulk density is disposed in a drop section of a conveyingline being connected to the release opening of the calcination device.It is not obligatory that the measuring device is in the direct vicinityof the calcination device, as the heat-treated material can be conveyedto the measuring device via appropriate conveying means such asconveying belts or screw conveyors. However, due to the design of themeasuring container, it is required that the measuring device isdisposed in a drop section of the conveying system, so that theheat-treated material can flow through the openings in the base surfaceof the measuring container.

BRIEF DESCRIPTION OF THE FIGURES

A detailed description of a method according to the invention and adevice according to the invention now follows. In the figures:

FIG. 1 shows a schematic image of a system for expansion of a sand-grainshaped raw material with a device for measuring bulk density,

FIG. 2 shows a detailed view of the device for measuring bulk density,

FIG. 3 shows a schematic image of a system for heat treatment of agrain-shaped feed material with a device for measuring bulk density.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION

FIG. 1 shows a system for expansion of sand grain-shaped raw material 1.In this case, the raw material 1 falls through a vertical shaft 4 whichcan be heated by means 2 for forming a temperature profile 3, in thepresent embodiment a plurality of electrical resistance heaters 2 areused. The raw material is fed in the head region 15 of the shaft 4.Since the resistance heaters 2 can be controlled individually, aspecific temperature profile 3 can be established along the shaft 4. Asa result of the thermal radiation which acts on the raw material 1 fromthe shaft 4, the raw material 1 expands to form expanded granulate 6.Due to the heated walls of the shaft 4 and the ensuing process air 16, ashaft flow 5 is established in the shaft 4.

An additional extraction device 24 is provided in the head region 15 ofthe shaft 4, which extracts process air 16 from the head region 15 andthus stabilizes the shaft flow 5. In addition, a control loop 25 iscoupled to the additional extraction device 24 which regulates thefraction of extracted process air 16 and sucked-in ambient air.Likewise, process air 16 can be blown into the head region 15 tostabilize the shaft flow 5 either by this additional extraction device24 or by another device not shown here.

Located at the lower end of the shaft 4 is a dosing element 14 whichregulates the quantity of granulate 6 conveyed from the shaft 4 into thepneumatic conveying line 7. In alternative embodiments, this dosingelement 14 is not provided, with the result that the shaft 4 opensdirectly into the conveying line 7.

An extraction device 9, which is preferably designed as a fan, ismounted at one end of the pneumatic conveying line which sucks ambientair from the other end of the conveying line 7, which is designed to beopen to the atmosphere and thus conveys expanded granulate 6. A gascyclone 10 is located inside this conveying line 7 via which granulate 6is separated from the conveying line. Located in the conveying line 7 isa filter system 22 which is preferably disposed between gas cyclone 10and extraction device 9 which separates small particles from theconveying line 7. By measuring the differential pressure by means of anadditional measuring device 23, the conveyed quantity of the extractiondevice 9 is controlled so that the flow velocity in the conveying line 7remains constant even when the filter system 22 is contaminated.

FIG. 2 shows a detailed view of a device 200 for measuring bulk densityof the expanded granulate 6 which is separated from the conveying line 7as a granulate flow 11 by means of a separating device, here designed asa gas cyclone 10, which is connected to the pneumatic conveying line 7.In this embodiment a measuring container 212 is mounted underneath thegas cyclone 10 in the operating state, which receives at least a part ofthe granulate flow 11 which is separated from the conveying line 7 inthe gas cyclone 10. In order to concentrate this granulate flow 11, afunnel 218 is located between the gas cyclone 10 and the measuringcontainer 212. Preferably the longitudinal axes of the gas cyclone 10,the funnel 218 and the measuring container 212 coincide to form oneaxis. The part of the granulate flow 11 which cannot be received by themeasuring container 212 can escape from this by means of an overflow 220over the edge of the measuring container 212. The measuring container212 is connected via a side arm 219 to the measuring device which isdesigned as a weighing device 213. By determining the weight in theweighing device and the known volume of the measuring container 212, thebulk density of the expanded granulate 6 can thus be measuredcontinuously. If deviations from the desired bulk density aredetermined, the temperature profile 3 of the shaft 4 is modified byreference to empirical values or the quantity of raw material fed to theshaft 4 is reduced on the basis of empirical values or both thetemperature profile is modified and the quantity of raw material fed tothe shaft 4 is reduced on the basis of empirical values.

FIG. 2 also shows that the measuring container 212 has a plurality ofopenings 221 in its base surface through which a part of the granulateflow 11 drains continuously. These openings 221 can have any shape, forexample, rectangles, slots, or squares, where in particular circularopenings 221 are preferably used.

Typical granule diameters of the expanded granulate 6 lie in the rangeof 0.5 to 5 mm. In order to ensure a continuous flow through themeasuring container 212, the ratio between the granule diameter and thediameter of the openings 21 is preferably between 1:3 and 1:100,particularly preferably between 1:5 and 1:50, in particular between 1:5and 1:25. For example, for a granule diameter of 2 mm and a factor of30, a ratio of 1:10, the diameter of the openings 21 is obtained as 2mm×10 as 20 mm.

FIG. 3 shows an alternate embodiment of a system in which the materialdirected into the measuring container 212 is not an expanded granulate 6produced by a vertical heated shaft 4, but a grain-shaped heat-treatedmaterial 152 which is produced by a calcination device 100.

In order to remove water of crystallization or carbonate from agrain-shaped, preferably pre-refined, feed material 142, such ascarbonated ore/minerals or hydrated ore/minerals, a first material flow140 containing the feed material 142 is fed into the calcination device100, in which it undergoes a heat treatment in order to achieve athermal decomposition of the material within the calcination device 100.At the end of the heat treatment process a second material flow 150containing the heat-treated material 152 is released from thecalcination device 100 and fed into the device 200 for measuring bulkdensity, the design and functionality of which is described in detailwith regard to FIG. 2. As the second material flow 150 containing theheat-treated material 152 is directly fed into the measuring container212 of the device 200, which measuring container 212 is disposedadjacent to and underneath of a release opening 130 of the calcinationdevice 100, no separation device is necessary compared to the embodimentdescribed in FIG. 2. As mentioned before, the second material flow 150is concentrated via funnel 218 before it is directed into the measuringcontainer 212. Furthermore the embodiment of the device 200 depicted inFIG. 3 is housed in a housing 230 in order to guide the part of thesecond material flow 150, which does not flow through the measuringcontainer 212, to an outlet opening 232, from which the second materialflow 150 can be conveyed to a packaging station or a further processingstation.

In the present embodiment the calcination device 100 comprises a rotarykiln 110, in which the heat treatment is carried out, which rotary kiln110 has a feed opening 120 for receiving the first material flow 140containing the feed material 142 and the release opening 130 forreleasing the second material flow 150 containing the heat-treatedmaterial 152 into the device 200. The calcination device 100 furthercomprises a feeding hopper 160, in which the feed material 142 isinserted, and a screw conveyor 170, which continuously conveys the feedmaterial 142 from the feeding hopper 160 to the feed opening 120 thuscreating the first material flow 140.

The method and the system described above are especially suitable forheat treatment of kaoline (terra alba), dolomite, gypsum or aluminiumhydroxide.

REFERENCE LIST

-   -   1 Sand grain-shaped raw material    -   2 Means for forming a temperature profile (resistance heaters)    -   3 Temperature profile    -   4 Shaft    -   5 Shaft flow    -   6 Expanded granulate    -   7 Pneumatic conveying line    -   8 Conveying flow    -   9 Extraction device    -   10 Gas cyclone    -   11 Granulate flow    -   14 Dosing element    -   15 Head region    -   16 Process air    -   22 Filter system    -   23 Additional measuring device    -   24 Additional extraction device    -   25 Control loop    -   100 Calcination device    -   110 Rotary kiln    -   120 Feed opening    -   130 Release opening    -   140 First material flow    -   142 Grain-shaped feed material    -   150 Grain-shaped heat-treated material    -   152 Second material flow    -   160 Feeding hopper    -   170 Screw conveyor    -   200 Device for measuring bulk density    -   212 Measuring container    -   213 Measuring device217 Base surface    -   218 Funnel    -   219 Side arm    -   220 Overflow    -   221 Openings    -   230 Housing    -   232 Outlet opening

What is claimed is:
 1. A system for heat treatment of a grain-shapedfeed material comprising: a calcination device that is designed toperform a heat treatment on the grain-shaped feed material being fedinto a first end of the calcination device in order to producegrain-shaped heat-treated material by removing water of crystallizationand/or carbon dioxide from the grain-shaped feed material, wherein thecalcination device has a feeding opening for receiving a first materialflow containing the grain-shaped feed material and a release opening forreleasing a second material flow containing the grain-shapedheat-treated material; and a device for measuring the bulk density ofthe grain-shaped heat-treated material comprising, at least onemeasuring container for receiving at least a part of the second materialflow, wherein the at least one measuring container has a base surfacehaving openings in order to allow at least a part of the received secondmaterial flow to drain continuously from the at least one measuringcontainer, a weighing device being connected to the at least onemeasuring container for continuously measuring the weight of thegrain-shaped heat-treated material flowing through the at least onemeasuring container in order to determine the bulk density of thegrain-shaped heat-treated material flowing through the at least onemeasuring container and to detect deviations from a desired bulk densityof the grain-shaped heat-treated material.
 2. The system according toclaim 1, wherein a means for concentrating the second material flow isdisposed between the release opening of the calcination device and theat least one measuring container.
 3. The system according to claim 2,wherein the means for concentrating the second material flow isconfigured as a funnel.
 4. The system according to claim 1, wherein thecalcination device comprises a rotary kiln.
 5. The system according toclaim 1, wherein the device for measuring the bulk density is disposedadjacent to the release opening of the calcination device.
 6. The systemaccording to claim 1, wherein the device for measuring the bulk densityis disposed underneath the release opening of the calcination device. 7.The system according to claim 1, wherein the device for measuring thebulk density is disposed in a drop section of a conveying line beingconnected to the release opening of the calcination device.
 8. Thesystem according to claim 1, wherein the measuring container isconnected via a side arm to the weighing device.
 9. The system accordingto claim 1, wherein an overflow for at least one part of the granulateflow is provided on the measuring container.
 10. The system according toclaim 1, wherein the weighing device is configured as scales.